This invention relates to automated manufacture of integrated circuits and more particularly to a carrier for use in tape-assisted bonding (TAB) of an integrated circuit chip onto a segment of a strip of flexible film material on which an array of flexible, conductive beam leads have been formed.
U.S. Pat. Nos. 4,007,479 and 4,069,496 to Kowalski generally describe the prior art techniques for tape-assisted bonding. Each of these patents discloses a different form of carrier in which a segment of a film strip is mounted for subsequent processing after the segment has been detached from a continuous strip of such segments.
Kowalski '479 discloses a fixture or carrier in the form of upper and lower layers, each in the form of a rectangular frame member, interconnected along one side of each of the frame members by a hinge. The frame members and hinge structure are integrally formed of plastic by injection molding. One of the layers has a rectangular cavity for receiving the segment of film strip. The cavity is formed to closely match the dimensions of the film strip. Lugs are formed in opposite lateral sides of the cavity for fitting into sprocket holes in the film strip. The frame members have openings to expose the film strip on both sides. The frame members are fastened together in overlying relationship by means of opposed concentric rings on the opposed faces of the upper and lower layers. The rings are arranged and sized to frictionally engage when nested together.
Kowalski '496 recognized that the design in the '479 patent had a number of problems and deficiencies. The '496 patent discloses a carrier or fixture composed of a single frame member having a rectangular cavity and specially formed lugs which insert through sprocket holes in the film segment. The lugs have overlapping lateral projections which are intended to retain the film segment in the carrier.
U.S. Pat. No. 4,547,794 to Tang also discloses a carrier and discusses the problems noted by Kowalski but which Tang deemed to remain unsolved. Tang proposes a carrier composed of a single frame member with a rectangular cavity for retaining a film segment. Formed integrally in the sides of the frame member are a plurality of enlongated cantilevered beam members which are movable from a first position to a second position for insertion and removal of the film segment in the cavity. These beam members are integrally formed with the frame members by plastic injection molding.
Another form of carrier is supplied commercially by AMS to Digital Equipment Corp. This carrier also is composed of a single frame member having a rectangular cavity for receiving a film strip segment. This carrier differs somewhat from the above-described carriers in that it does not have lugs for insertion into the film sprocket holes. Instead, it has diagonally-oriented square lugs positioned for insertion into special positioning holes located at the four corners of each segment just inward of the sprocket holes. This arrangement is in accordance with a set of standards known as the JEDEC Standards, adopted by a group of U.S. integrated circuit manufacturers. The film segment is secured in each mount by means of four small plastic pins which are frictionally inserted into four holes in the bottom wall of the cavity of the frame member at each corner of the segment The holes are positioned in the bottom wall of the carrier so as to align with the sprocket holes in each corner of the film segment. The pins are sized to an interference fit with the holes and have a cap which overlaps the film around each sprocket hole.
From a review of the foregoing patents, it is apparent that there is a need for a reliable method and form of carrier for mounting segments of flexible film strips or tape-assisted bonding of integrated circuits. Meeting this objective entails solving a number of rather difficult problems unique to handling integrated circuits. Moreover, the problems become increasingly difficult as the circuitry gets more complex. The examples of film segments in the Kowalski patents show circuit connections on which 40 beam leads have been formed, 10 per side. Current integrated circuit technology often calls for circuits having hundreds of beam leads. This means the beam leads must be narrower and closer together (i.e. narrower pitch) by nearly an order of magnitude compared to those shown in Kowalski. Lateral alignment is critical to ensure bonding of the beam leads to the correct locations on the integrated circuit chips.
Retaining alignment uniformly throughout each step of the process and from one carrier to the next is critical to automated processing. The film strip segments must be securely held in place for various processing steps while providing access to the beam leads for testing the connections and circuit but permit easy placement of the segment in the carrier and removal of it from the carrier after processing. The design of the carrier should permit all processing steps to be performed mechanically in a fully automated process, with a high degree of reliability.
Prior carriers do not meet these requirements sufficiently for state-of-the-art integrated circuits. Accordingly, a need remains for an improved carrier.